On Mon, May 06, 2019 at 08:14:12PM -0700, Frank Rowand wrote: > On 5/1/19 4:01 PM, Brendan Higgins wrote: > > ## TLDR > > > > I rebased the last patchset on 5.1-rc7 in hopes that we can get this in > > 5.2. > > > > Shuah, I think you, Greg KH, and myself talked off thread, and we agreed > > we would merge through your tree when the time came? Am I remembering > > correctly? > > > > ## Background > > > > This patch set proposes KUnit, a lightweight unit testing and mocking > > framework for the Linux kernel. > > > > Unlike Autotest and kselftest, KUnit is a true unit testing framework; > > it does not require installing the kernel on a test machine or in a VM > > and does not require tests to be written in userspace running on a host > > kernel. Additionally, KUnit is fast: From invocation to completion KUnit > > can run several dozen tests in under a second. Currently, the entire > > KUnit test suite for KUnit runs in under a second from the initial > > invocation (build time excluded). > > > > KUnit is heavily inspired by JUnit, Python's unittest.mock, and > > Googletest/Googlemock for C++. KUnit provides facilities for defining > > unit test cases, grouping related test cases into test suites, providing > > common infrastructure for running tests, mocking, spying, and much more. > > As a result of the emails replying to this patch thread, I am now > starting to look at kselftest. My level of understanding is based > on some slide presentations, an LWN article, https://kselftest.wiki.kernel.org/ > and a _tiny_ bit of looking at kselftest code. > > tl;dr; I don't really understand kselftest yet. > > > (1) why KUnit exists > > > ## What's so special about unit testing? > > > > A unit test is supposed to test a single unit of code in isolation, > > hence the name. There should be no dependencies outside the control of > > the test; this means no external dependencies, which makes tests orders > > of magnitudes faster. Likewise, since there are no external dependencies, > > there are no hoops to jump through to run the tests. Additionally, this > > makes unit tests deterministic: a failing unit test always indicates a > > problem. Finally, because unit tests necessarily have finer granularity, > > they are able to test all code paths easily solving the classic problem > > of difficulty in exercising error handling code. > > (2) KUnit is not meant to replace kselftest > > > ## Is KUnit trying to replace other testing frameworks for the kernel? > > > > No. Most existing tests for the Linux kernel are end-to-end tests, which > > have their place. A well tested system has lots of unit tests, a > > reasonable number of integration tests, and some end-to-end tests. KUnit > > is just trying to address the unit test space which is currently not > > being addressed. > > My understanding is that the intent of KUnit is to avoid booting a kernel on > real hardware or in a virtual machine. That seems to be a matter of semantics > to me because isn't invoking a UML Linux just running the Linux kernel in > a different form of virtualization? > > So I do not understand why KUnit is an improvement over kselftest. > > It seems to me that KUnit is just another piece of infrastructure that I > am going to have to be familiar with as a kernel developer. More overhead, > more information to stuff into my tiny little brain. > > I would guess that some developers will focus on just one of the two test > environments (and some will focus on both), splitting the development > resources instead of pooling them on a common infrastructure. > > What am I missing? kselftest provides no in-kernel framework for testing kernel code specifically. That should be what kunit provides, an "easy" way to write in-kernel tests for things. Brendan, did I get it right? thanks, greg k-h
